Preventing excessive gestional weight gain in overweight and obese women has the potential to reduce women's risk of obesity, as well as the risk of obesity in their children. Within the Kaiser Permanente Northern California (KPNC) health system, we propose a randomized controlled clinical trial of diet and physical activity (PA) to help overweight/obese pregnant women achieve appropriate gestational weight gain (GWG). Participants will be randomly assigned to a lifestyle intervention or usual medical care (200 women in each arm; 25% White, 25% African Americans, 25% Asians and 25% Hispanic). The sample will be selected from among women with body weight measured by a KPNC provider no more than 12 months prior to conception. Women will be enrolled at 10 wks of pregnancy. The intervention will begin at 12 wks. It will be delivered via 2 in-person counseling sessions and 11 telephone contacts with study dieticians trained in motivational interviewing techniques who are housed at the KPNC Perinatal Center. Cost-effectiveness analyses will be performed. The intervention will be designed and evaluated for possible translation and adoption by the health care system. Women and their infants will be followed for 12-m after delivery. Study measurements, assessed by trained study personnel blinded of treatment assignment, will be collected at 10-wks and 32-wks of pregnancy, at delivery and at 6-m and 12-m postpartum. Infant measurements will take place at birth and at 6- m and 12-m of age. The PRIMARY AIM is to help overweight/obese pregnant women achieve appropriate total gestional weight gain according to their prepregnancy BMI and weeks of pregnancy, as recommended by the Institute of Medicine (IOM). Primary outcomes will be the proportion of women with appropriate Total GWG and the Rate of Maternal GWG. The secondary outcome will be the proportion of infants with appropriate for gestational age (AGA) birthweight. SECONDARY AIMS include assessing whether women assigned to the lifestyle intervention, as compared to usual care, have: a) more favorable changes in the percent of calories from fat, minutes of PA per week and body fat mass during pregnancy; b) more favorable changes in weight and body fat mass at 12-m postpartum; c) have infants with more appropriate anthropometrics at 12-m. EXPLORATORY AIMS include exploration of the associations between the GWG intervention and women's cardiometabolic profiles and infants' cardiometabolic profiles and body fat mass. Exploring possible associations of GWG management with adiposity and cardiometabolic profiles will provide valuable information for obesity prevention efforts. The potential adoption of a GWG management program by an integrated health care system represents a unique opportunity for interrupting the vicious cycle of obesity and cardiometabolic complications.